In general, color reproducibility is measured using a color rendering index (CRI). The CRI of sunlight is about 100, the CRI of an incandescent lamp is about 95, and the CRI of a fluorescent lamp is about 70 to 80. A light emitting diode is a semiconductor device having well-known light emitting properties. Such a light emitting diode excites electrons across a band gap between a valence band and a conductive band of a semiconductor active layer and thus emits light. Here, light of a wavelength band depending on the band gap may be emitted. That is, color of light emitted from the light emitting diode depends on a semiconductor material of the active layer of the light emitting diode.
For example, an emission spectrum of the light emitting diode is generally concentrated only on one wavelength band. This is suitable for some applications but is not suitable for other applications, for example, the case in that the emission spectrum emits light providing a very low CRI.
Since white light requires mixing of at least two colored lights, only one light emitting diode may not produce white light. As one example, when three light emitting diodes emitting red, blue and green lights are used, white light may be produced. As another example, if one light emitting diode emitting blue light is provided and a luminescent material, such as a phosphor, emits yellow light in response to excitation of light emitted from the blue light emitting diode, white light may be produced by mixing blue light and yellow light. Such a luminescent material may be present in an encapsulating member to encapsulate the light emitting diode.
In general, a 1976 CIE chromaticity diagram is a useful index to define colors through weighted sums of colors. Recently, demand for lighting apparatuses including light emitting diodes, i.e., solid state light emitting units having higher energy efficiency, an enhanced CRI, enhanced efficiency (lm/W), and a longer lifespan, has increased. However, when a light source is manufactured, the CRI of the light source is fixed and thus may not be tuned.